This invention, which resulted from a contract with the United States Department of Energy, relates to a system for monitoring the operation of a laser beam used for cutting or other purposes.
The use of a laser beam to cut spent nuclear fuel elements into pieces has led to the development of optical systems for directing a laser beam into a sealed radiation-shielding chamber and focusing the beam at a predetermined point therein, as exemplified by the laser beam alignment system disclosed in U.S. patent application Ser. No. 352,744, filed by Kasner et al on Feb. 26, 1982, and assigned to the assignee of this application, the United States Department of Energy. There has continued to be a need, however, for a simple and trustworthy means for detecting the placement of an obstruction in the path of a laser beam used for cutting a fuel element, after the laser beam has been properly aligned and focused and cutting has commenced. It has been proposed heretofore to use an infrared detector for this purpose, the detector being located in the chamber in which fuel elements are cut. However, the response time required for an infrared detector so located to terminate the operation of a laser cell, if the path of the laser beam is blocked, is excessive from the standpoint of safety in controlling the cutting operation. Location of an infrared sensor inside a radiation-shielding chamber also creates difficulties in routing and handling the electric cable that must extend from the sensor to a point outside the chamber.